Angular displacement transducers, which produce an electrical signal indicative of the rotational angle of a part, such as a shaft, are widely used in industry. Various designs of incremental and absolute optical encoders as well as electromagnetic or inductive angle sensors, also known as "resolvers", are known. Optical encoders tend to be expensive, fragile and/or have low angular resolutions.
Some electromagnetic angular displacement transducer designs involve mounting a winding on the rotating part adjacent a stationary winding. As the rotating winding turns the electromagnetic coupling between the stationary and rotating windings changes. This, in turn, changes an electrical potential induced in one of the windings by a signal in the other winding. The geometry of these devices generally causes such devices to produce an electrical output which varies sinusoidally with angle.
There are several problems which prior art angular displacement transducers typically share in various combinations. One problem is that accurate transducers according to prior art designs are complicated and expensive to make. A second problem with some prior art angular displacement transducers is that they the relationship between the electrical output signal and the angle being measured can not be easily derived from simple calculations. Many such transducers cannot produce an analog output which varies linearly with angle. As noted above, most such analog transducers produce an output that varies sinusoidally with angle. A third problem is that the prior art does not provide a good selection of angular transducers that can be placed in the center of a shaft and are reasonable in both cost and accuracy. A fourth problem is that most prior art transducers are not easily capable of resolving the relative angular displacement of two shafts. A fifth problem is that many prior art angular displacement transducers are fragile and/or do not work well when wet. Such transducers are not readily usable in settings where there is significant vibration or moisture.
There is a need for simple, rugged, accurate angular displacement transducers. There is a particular need for simple accurate rugged angular displacement transducers which produce output signals which bear a linear relationship to the angle being measured. There is also a need for simple, rugged, accurate angular displacement transducers which produce output signals which bear sinusoidal or other relationships to the angles being measured.